A developing device known in the art (see Japanese Patent Application Publication No. 2010-164736, for example) is provided with a housing, a developing roller rotatably supported in the housing, a thickness-regulating blade having a rubber blade part that contacts the circumferential surface of the developing roller, and sealing members disposed between the housing and the two axial ends of the developing roller. In particular, the sealing members are shaped to conform to the circumferential surface of the developing roller. One end of each sealing member in the rotating direction of the developing roller is in contact with the corresponding end face of the rubber blade part in the axial direction thereof.